title: Betulinic acid binding to human serum albumin: a study of protein conformation and binding affinity.
abstract: Betulinic acid (BA) has anti cancer and anti-HIV activity and has been proved to be therapeutically effective against cancerous and HIV-infected cells. Human serum albumin (HSA) is the predominant protein in the blood. Most drugs that bind to HSA will be transported to other parts of the body. Using micro TOF-Q mass spectrometry, we have shown, for the first time that BA isolated from a plant (Tephrosia calophylla) binds to HSA. The binding constant of BA to HSA was calculated from fluorescence data and found to be K(BA)=1.685+/-0.01 x 10(6) M(-1), indicating a strong binding affinity. The secondary structure of the HSA-BA complex was determined by circular dichroism. The results indicate that the HSA in this complex is partially unfolded. Further, binding of BA at nanomolar concentrations of BA to free HSA was detected using micro TOF-Q mass spectrometry. The study revealed a mass increase from 65199 Da (free HSA) to 65643 Da (HSA+drug), where the additional mass of 444 Da was due to bound BA. Based on the results of this study, it is suggested that micro TOF-Q mass spectrometry is useful technique for drug binding studies.
authors.affiliation: Department of Biochemistry, School of Life Sciences, University of Hyderabad, Hyderabad 500046, India. psrajagopal@yahoo.com
authors.forename: Rajagopal
authors.initials: R
authors.lastname: Subramanyam
authors.forename: Anilkishor
authors.initials: A
authors.lastname: Gollapudi
authors.forename: Persis
authors.initials: P
authors.lastname: Bonigala
authors.forename: Madhurarekha
authors.initials: M
authors.lastname: Chinnaboina
authors.forename: Damu G
authors.initials: DG
authors.lastname: Amooru
mesh_terms: D002942:Circular Dichroism; D006801:Humans; D053978:Pentacyclic Triterpenes; D011485:Protein Binding; D017433:Protein Structure, Secondary; D012709:Serum Albumin / Q000737:chemistry* / Q000378:metabolism; D013053:Spectrophotometry; D014315:Triterpenes / Q000737:chemistry* / Q000378:metabolism; D000094062:Betulinic Acid
chemical_list: D053978:Pentacyclic Triterpenes; D012709:Serum Albumin; D014315:Triterpenes; D000094062:Betulinic Acid